Optical-coherence reflectometry (OCDR) was first introduced as a method for high-resolution probing of reflections from components of fiber-optic systems. We have been exploring the applications of this technique to imaging and to characterization of biological tissues. Using prototype instruments built in our laboratory, we have succeeded in imaging subsurface structures in living skin and other tissues. To help understand the limits of contrast and resolution that can be attained with this new type of microscopy, mathematical models of the propagation of partially coherent light in dense tissue have been constructed and tested in experiments on tissues and tissue phantoms. Our results show that without staining or modifying a tissue in any way, structures embedded 1 mm to 2 mm in skin tissue can be imaged with a resolution of about 10 mm.